Nonradiating Silicon Nanoantenna Metasurfaces as Narrowband Absorbers

High-refractive-index (HRI) nanostructures support optically induced electric dipole (ED) and magnetic dipole (MD) modes that can be used to control scattering and achieve narrowband absorption. In this work, a high-absorptance device is proposed and realized by using amorphous silicon nanoantenna (a-Si NA) arrays that suppress backward and forward scattering with engineered structures and in particular periods. The overlap of ED and MD resonances, by designing an array with a specific period and exciting lattice resonances, is experimentally demonstrated. The absorptance of a-Si NA arrays increases 3-fold in the near-infrared range in comparison to unpatterned silicon films. Nonradiating a-Si NA arrays can achieve high absorptance with a small resonance bandwidth (Q = 11.89) at a wavelength of 785 nm. The effect is observed not only due to the intrinsic loss of material but by overlapping the ED and MD resonances.